>perl -wMstrict -le
"package L;
   use vars qw(%lone);
   our %once;
   sub l { return print __PACKAGE__, qq{: @_} }
 package main;
   print 'do some stuff in ', __PACKAGE__;
 package L;
   use vars qw(%singular);
   our %onetime;
 package main;
   $L::once{x}     ||= (L::l('hi from',     __PACKAGE__), 1);
   $L::lone{x}     ||= (L::l('hello from',  __PACKAGE__), 1);
   $L::onetime{x}  ||= (L::l('hiya from',   __PACKAGE__), 1);
   $L::singular{x} ||= (L::l('greets from', __PACKAGE__), 1);
   $L::once{foo} ||= L::l('this should print');
   $L::once{foo} ||= L::l('but this should NOT print!');
"
do some stuff in main
L: hi from main
L: hello from main
L: hiya from main
L: greets from main
L: this should print